Cell division is one of the most fundamental and challenging processes in the life of bacteria. The divisome is a complex composed primarily of membrane proteins that assembles at mid-cell and is necessary for bacterial cell division to occur. The structural architecture of the divisome, and the organization of its transmembrane region in particular, are still mysterious. Unraveling this organization is a crucial goal for a ful understanding of the mechanisms that are involved in bacterial division and its regulation. This goal of this proposal is a structural and functional analysis of six single-span transmembrane proteins (ZipA, FtsL, FtsB, FtsQ, FtsI and FtsN) that are central to the assembly of the divisome. The proposed approach is multi-disciplinary, with a biophysical characterization of the interactions in vitro, mutagenesis, computational modeling and X-ray crystallography to study their extra-membranous domains. Our main objectives are to determine the ability of the transmembrane region of the six divisomal proteins to interact; measure the energetics of their association; and determine their structural organization. This project addresses a critical barrier to progress in understanding bacterial cell division, namely the lack of information on the structural organization of the membrane region of the divisiome. By beginning to unravel the structural and mechanistic details of the complex, this project will establish important groundwork needed for the development of new strategies for understanding and controlling bacterial growth.